Coral Atolls

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What immediately comes to mind when many of us think of an atoll is a
desolate, circular array of coral reefs with white, sandy islands
populated by a few lonely, swaying palm trees and perhaps a castaway or
two. Were we to consider them more closely, however, we would find that
this standard perception just skims the surface. Atolls are, in fact,
some of the most complex and vibrant structures on the planet. Built
diligently over thousands of years by tiny, sea anenome-like coral
polyps, these ring shaped coral structures can be tens of kilometers in
diameter with individual reefs large enough to support lush tropical
islands and even small cities. As is the case with any living coral
structure, countless species of fish and invertebrates can be found
inhabiting the waters in and around an atoll. But unlike the fringing
reefs along Florida’s coast or even the barrier reefs off the shore of
Australia, atolls do not border anything. Instead, they sit on a coral
base that often rises thousands of meters from the ocean’s floor in some
of the most remote areas of the tropical oceans.

The top picture is a true-color image from the Enhanced Thematic
Mapper Plus (ETM+) aboard Landsat 7. The middle photograph shows a reef and the flat,
forested interior of an island in the Maldives. The bottom photograph demonstrates
the diversity of life in and around coral reefs.

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This image originally appeared on the Earth Observatory. Click here to view the full, original record.